Pre-Colombian Jamaica: Caribbean Archeology and Ethnohistory

78 / Chapter 6.
heights painstakingly worked out for each of the mapped sites by Lee (North,
East, and Elevation) followed this system. Using his figures, the sites can be located
on any of the old maps, which are still frequently used in Jamaica. Between
1982 and 1991, a new series of 1:50,000 scale topographic maps was issued
in 20 numbered sheets covering the entire island (Fincham 1997:Figure
1B). This series is metric, that is, it employs kilometers and meters for both the
grid and the contours, and it is generally used in newer works describing locations
on the island (e.g., Donovan et al. 1995). As pointed out by Edward Robinson,
“the projection is the same for the two systems,” hence, “converting from
one to the other is a relatively simple matter in principle” (Robinson 1996). The
standard conversion formula is:
X (eastings) metric = (X imperial × .3048) + 82,360
Y (northings) metric = (Y imperial × .3048) + 28,080
This formula has been applied to all of Lee’s figures, so new island grid references
and elevations in meters are available for all the sites, in addition to Lee’s
original measurements.
While the positions of the sites can be and have been accurately recorded
on the published maps of Jamaica using the above coordinates, it must be
pointed out that there is a discrepancy between the conventional Jamaican grid
and the worldwide electronic grid now used by geographic information system
(GIS) surveyors. Account needs to be taken of this in the fi eld if GPS equipment
is used. The situation is fully explained by authors included in the References
Cited in this volume (Miller 2003; Mugnier 2003; Stewart 2002, 2003a,
2003b). Briefly, the problem arises because, as Miller puts it, in the past “spheroids
of different dimensions have been used to represent the earth,” and these
do not completely coincide with the ellipsoid which, as Stewart says, now constitutes
the “world standard.” This is known as WGS, or World Geodetic System
84. The projection used for the Jamaican 1:50,000 grid is known as Clarke
1866. It has its “true” origin at 18° North and 77° West. This point is to the
west of Spanish Town. In order to avoid map positions being recorded both as
“minuses” and as “pluses,” it was arbitrarily moved to a “false” origin, which in
the metric version is situated 250 km west and 150 km south. All the site locations
mentioned above are by reference to this arbitrary origin and they all appear
as “pluses.” The “true” Jamaican grid origin, as Stewart says, occurs at a
point about 311 m north- northeast of the point that WGS 84 would determine
as the correct position for 18° North and 77° West. That is the extent of the
discrepancy. Stewart’s advice for GPS users is to “collect data in WGS 84 and